The subject of the invention relates to the field of rotary movement sensors in the general sense, and is advantageously targeted at contactless rotary movement sensors, characterized by the absence of a mechanical connection between at least one sensitive detection cell and the part whose position, movement, speed or acceleration they measure.
The subject of the invention is more specifically targeted at contactless movement sensors in which the coupling between the moving part and the sensitive cell is established via a magnetic electromagnetic or electrostatic field, the strength of this coupling depending on the relative position of the part and of the sensor.
The subject of the invention finds a particularly advantageous application in the field of contactless rotary movement sensors employing sensitive detection cells of the Hall-effect type.
In the field of contact-type rotary movement sensors, for example of the potentiometer type, a sensor comprises a rotor fitted with brushes that rub along conductive tracks formed on a stator. The rotor is equipped with means of connection or assembly with a drive shaft of a part whose position and/or movement are to be detected.
In the technical field of contactless rotary movement sensors, of the magnetic type, it is known practice for a sensor to be produced that comprises a stator equipped with one or more cells sensitive to magnetic induction or to a variation in magnetic induction, such as Hall-effect cells. Such a sensor also comprises a rotor equipped with a moving target provided with magnetic elements and delimiting at least one coupling gap with the sensitive cells. The detection cells are capable of delivering a signal which is a function of the position and/or movement of the moving element. Conventionally, the rotor of such a sensor is provided with means of connection to a drive shaft of a part whose position and/or movement are to be detected.
A rotary movement sensor of the contact or contactless type requires a mechanical connection to be made, via connecting means, between the rotor and the drive shaft exhibited by the part whose position and/or movement is to be detected. For example, the rotor is generally equipped, by way of connecting means, with a housing which complements the cross section of the drive shaft and which may be of D or I shape.
The mounting of such a sensor consists in making the mechanical connection between the rotor of the sensor and the moving shaft and fixing the casing of the sensor to the support associated with the part whose movement is detected. It has come to light that mounting such a sensor poses a certain number of difficulties. Specifically, it needs to be taken into consideration that, bearing in mind the manufacturing tolerances and functional clearances, there may be a misalignment of the rotor compared with the drive shaft, leading to a change in the position of the rotor with respect to the stator.
For a rotary movement sensor of the contact type, for example of the potentionmeter type, for which the brushes connected to the rotor rub on tracks connected to the stator, this results in operation under abnormal conditions, leading to rapid deterioration, even if the operation of such a sensor is not adversely affected in so far as the electrical contact is still made.
For connectionless rotary movement sensors, particularly magnetic sensors, an axial or radial offset of the rotor with respect to the stator alters the characteristics of the magnetic circuit, particularly as far as the gaps and magnetic leaks are concerned. The variation in the gap of the magnetic circuit leads to a variation in the electric signal delivered by the sensor leading, in particular, to a drop in the linearity of the signal or to a change in the gradient expressing the voltage as a function of the angle through which the rotor has rotated.